The disclosure relates to a method of using surface protection films to adhere to and protection of smooth surfaced substrates.
Surface protection films, also known as masking films, are typically used to provide a physical barrier to prevent damage, contamination, scratching, scuffing, or other marring of a substrate to which they are adhered. Surface protection films may be used to provide such protection during manufacture, shipping, or storing prior to use of the substrate. Substrates used as optical components for televisions, computer monitors and other displays require surface protection films that are adhered to the surface of the substrate and then subsequently removed from the surface of the substrate without damaging the substrate or leaving residue, staining or other defects on the surface of the substrate. Substrates used as optical components by their nature require surfaces that are smooth, having a roughness of less than 0.0127 micron.
The manufacture and use of smooth surface substrates requires that the smooth surface substrates undergo a sequence of operations, such as cutting, coating, edge polishing, stacking, and shipping. The surfaces of the smooth surface substrate need to be protected during these operations, as well as during storage. Moreover, several of these processes, particularly the cutting and edge grinding operations, can increase the temperature of the substrate. As the temperature of the substrate increases, there is an increased risk that the surface protection film will adhere too strongly (peel force is more than 100 g/25 mm per the high temperature 70 deg. C. test method discussed herein) to the smooth surface substrate. In such cases, there is an increased risk that the surface protection film will tear or delaminate when it is removed, or will leave a residue on the smooth surface substrate or will stain the smooth surface substrate, all of which are detrimental. An example of a smooth surfaced substrate is Polymethylmethacrylate (“PMMA”) substrates used as a light guide plate in the back light assembly for LCD/LED panel manufacturing.
A balance in the surface protection film's performance properties is needed for a method of adhering a surface protection film to a smooth surface substrate to ensure that the surface protection film remains adhered to the smooth surface substrate surface during processing, yet the surface protection film does not adhere too strongly (peel force is more than 100 g/25 mm at 23 deg. C. and 70 deg. C.) to the smooth surface substrate such that the surface protection film leaves residue or other defects on the surface of the smooth surface substrate.
Also an issue is when known surface protection films containing pressure-sensitive adhesive layers adhere to the surface protection film itself when the surface protection film is wound on a roll or the adhesion layer otherwise contacts a portion of the surface protection film. This phenomenon, known as “blocking” can result in processing difficulties and can also result in the film tearing or delaminating as it is unwound, resulting in poor yields. In some instances, a release paper can be used to prevent blocking, but this adds to the cost, increases waste, and adds complexity to the manufacturing and use of the surface protection films. As such, there exists the need to have method of adhering a surface protection film to a smooth surface substrate wherein there is not a need to remove a release paper while providing a surface protection film that does not have issues with blocking.